I tried:

sub ext_s {        # Returns characters in sorted order
  my ($s) = @_ ;
  my %h ;
  @h{split(//, $s)} = undef ;
  return join('', sort keys %h) ;
} ;

sub ext_o {        # Returns characters in original order
  my ($s) = @_ ;
  my @h ;
  return join('', grep { !$h[ord($_)]++ } split(//, $s)) ;
} ;

[download]
compared to:
sub ext_dw {
  my ($s) = @_ ;
  my %h ;
  $h{$_} = undef foreach split(//, $s) ;
  return join('', sort keys %h) ;
} ;

sub ext_cn {
  my ($s) = @_ ;
  my %h ;
  $s =~ s/(.)/$h{$1}++?'':$1/ge ;
  return $s ;
} ;

[download]
and benchmarked:
      Rate   cn   dw    s    o
cn 10101/s   -- -40% -54% -59%
dw 16949/s  68%   -- -22% -31%
s  21739/s 115%  28%   -- -11%
o  24390/s 141%  44%  12%   --

In reply to Re: Collapsing a string to unique characters by gone2015
in thread Collapsing a string to unique characters by dwhite20899

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.